Fred,
While not having any direct experience with this sort of material, I
would expect that you would need to be extremely careful of possible
contamination (doping) at elevated temperatures. This means that
contaminated equipment might easily affect the resistivity of the
substrates.

Michael Pedersen
The MEMS Exchange

Fred Hussain wrote:
> Dear all,
>
> I am looking for silicon substrates which can be machined using conventional
> MEMS type processes, but at the same time are highly insulating. I've found
> a web page with silicon of 250Kohm-cm resistivity -
> http://www.tydex.ru/materials/materials2/Si.html.